This application is related to co-pending application U.S. serial number, filed concurrently herewith.
The present invention relates in general to a rear subframe for a multi-link vehicle suspension and, more specifically, to the articulating connection of control arms to a cast aluminum subframe.
The vehicle frame supports the vehicle body and, together with other components, such as control arms, springs, and shock absorbers, comprises the suspension system which permits up and down wheel movement without up and down movement of the body. Due to the many forces to which the frame is subjected, it is important that the frame have high stiffness. The vast majority of vehicle frames have been fabricated from steel because of its high strength, high stiffness, and reasonable cost. However, there are also concerns for minimizing the weight of a frame, based mainly on a desire to improve fuel economy.
Integral castings of aluminum or aluminum alloys may be used as vehicle frames or more typically subframes, cradles, and cross members (i.e., frame sections). Aluminum is able to provide good stiffness and can provide a significant reduction in weight. A hollow cross section (e.g., box or tubular) of the subframe members is used to further improve stiffness and reduce weight.
Control arms are swinging levers that provide the links between the subframe and the wheels (or more typically the steering knuckles attached to the wheels). The frame or subframe must provide articulating mounts for the control arms. A common type of control arm is known as the A-arm, in which each arm has two connection points with the subframe and one connection point with the wheel. The subframe articulations typically include a clevis arrangement.
In a clevis, it is necessary to include clearance between the flanges and the control arm bushing to permit insertion of the bushing between the flanges. After tightening of a clevis bolt, the flanges flex toward the bushing to close-off the clearance. In an aluminum casting, however, flexing of the flanges may lead to high stress.
The present invention has the advantage of providing an integrally cast aluminum subframe with control arm connections that avoid high stress in the connections.
In one aspect, the invention provides a subframe for a vehicle which is adapted to receive articulations (e.g., bushings) of control arms for attaching vehicle wheels. The subframe comprises a substantially hollow left side-rail, a substantially hollow right side-rail, a front cross-member, a rear cross-member, lower control arm connections on the left and right side-rails, a left-side upper control arm connection on one of the cross-members, and a right-side upper control arm connection on the one cross-member. At least one of the upper control arm connections comprises a respective mounting stud, the stud including a bore extending substantially parallel to the side-rails and adapted to secure at least one of the articulations of an upper control arm using a bolt, whereby the articulation is retained between a head of the bolt and the mounting stud.